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PubMed1979

Recent advances in programmable pacemakers. Consideration of advantages, longevity and future expectations.

The important electrical characteristics of conventional ventricular demand pacemakers currently widely employed are unable to be altered by noninvasive means after their implantation. However, a number of domestic pacemaker manufacturers have started to introduce a new modality for atraumatic modulation of these devices, the fully programmable pacemaker system, whereby the several variables regulating pacemaker operation may be optimized on an individual basis according to need. Such programmable pacemaker functions which can be varied include rate, energy output, refractory period and sensing threshold. The indications, significance and mechanisms for control of the various function programming are delineated for physician understanding at the present time.

Arrhythmias, Cardiac↗
PubMed1995

Authentic standards for the reductive-cleavage method. The positional isomers of partially methylated and acetylated or benzoylated 1,4-anhydro-D-xylitol.

Described herein is a general method for the synthesis of all positional isomers of methylated and acetylated or benzoylated 1,4-anhydro-D-xylitol. The benzoates are generated simultaneously from 1,4-anhydro-D-xylitol by sequential partial methylation and benzoylation or sequential partial benzoylation and methylation. The individual isomers are obtained in pure form by high-performance liquid chromatography. Debenzoylation and acetylation provided the corresponding acetates. The 1H NMR spectra of the benzoates and the electron ionization mass spectra of the acetates and the tri-O-methyl derivative are reported herein as are the linear temperature programmed gas-liquid chromatography retention indices of the acetates and the tri-O-methyl derivative on three different capillary columns.

Acetates↗
PubMed1995

Synthesis and characterization of authentic standards for the reductive-cleavage method. The positional isomers of partially methylated and acetylated or benzoylated 1,4-anhydro-L-fucitol.

Described herein is the synthesis of all positional isomers of methylated and acetylated or benzoylated 1,4-anhydro-L-fucitol. The benzoates are generated simultaneously from 1,4-anhydro-L-fucitol by sequential partial methylation and benzoylation or sequential partial benzoylation and methylation. The individual isomers are obtained in pure form by high-performance liquid chromatography. Debenzoylation and acetylation provided the corresponding acetates. The 1H NMR spectra of the benzoates and the electron-ionization mass spectra of the acetates and the tri-O-methyl derivative are reported herein as are the linear temperature programmed gas-liquid chromatography retention indices of the acetates and the tri-O-methyl derivative on three different capillary columns.

Acetates↗
PubMed1995

Authentic standards for the reductive-cleavage method. The positional isomers of partially methylated and acetylated or benzoylated 1,5-anhydro-D-glucitol.

Described is an efficient method for the synthesis of the sixteen positional isomers of methylated and acetylated or benzoylated 1,5-anhydro-D-glucitol. The compounds are generated simultaneously by partial methylation of 1,5-anhydro-D-glucitol and subsequent benzoylation, and the individual isomers are obtained in pure form by high-performance liquid chromatography. Debenzoylation of the latter and acetylation yielded the desired acetates. Reported are the 1H NMR spectra of the benzoates and the electron-ionization mass spectra of the acetates and the tetra-O-methyl derivative. Also reported for the acetates and the tetra-O-methyl derivative are their linear temperature programmed gas-liquid chromatography retention indices on three different capillary columns.

Acetates↗
PubMed1995

Synthesis and characterization of authentic standards for the analysis of ribofuranose-containing carbohydrates by the reductive-cleavage method.

Described herein is the synthesis of all positional isomers of partially methylated and acetylated or benzoylated 1,4-anhydro-D-ribitol. The benzoates are generated simultaneously from 1,4-anhydro-D-ribitol by sequential partial methylation and benzoylation or sequential partial benzoylation and methylation. The individual isomers are obtained in pure form by high-performance liquid chromatography. Debenzoylation and acetylation provided the corresponding acetates. Reported herein are the 1H NMR spectra of the benzoates and the electron-ionization mass spectra of the acetates and the tri-O-methyl derivative and also for the acetates and the tri-O-methyl derivative, their linear temperature programmed gas-liquid chromatography retention indices on three different capillary columns.

Acetates↗
PubMed1976

Improved method for measurement of serum levels of phenobarbital, carbamazepine, primidone and diphenylhydantoin by gas-liquid chromatography.

A gas-liquid chromatographic method for the simultaneous determination of phenobarbital, primidone, carbamazepine and diphenylhydantoin in human serum following therapeutic doses has been developed. After extraction with chloroform, the anticonvulsant drugs were methylated with phenyltrimethylammonium hydroxide in dimethylformamide at 85 degrees C for gas-liquid chromatography. Linear temperature programming of a 1% OV-17 column was used to achieve separation and quantitation. The procedure described in the present paper is relatively simple, highly specific and sufficiently sensitive for use in routine clinical assays.

Analysis of Variance↗
PubMed1980

A data validation program nucleus.

A data validation program designed for flexibility and user-modification is presented. It is assumed that the data to be validated consist of packets; i.e., groups of records with a common value in a record-linking field. Acceptance or rejection of data is on a packet basis. Individual field validation is specified by user-supplied tables. Multiple field checking and field interaction checking on both an intra-record and an inter-record basis may be specified by user-supplied subprograms. The program is written in PL/I using structured programming techniques. Further modifications such as record size and key positions are possible at pre-processor time.

Computers↗
PubMed1984

Evidence concerning a possible steady state rate equation for E. coli alkaline phosphatase.

Steady state data was obtained for alkaline phosphatase over a wide range of experimental conditions using two substrates, four inhibitors, two modifiers and several pH, ionic strength and temperatures values. The data was fitted by rational functions of degree 1:1, 2:2 and 3:3 using a non-linear regression program and then the F-test was used to assess the goodness of fit. A proportion of the curves could only be fitted by 2:2 functions but many of them could be adequately fitted by 1:1 functions. No statistically significant improvement in fit occurred with 3:3 functions. Data was simulated using a computer program to see what sort of curves could be generated by a two sites mechanism proposed for alkaline phosphatase and this study showed it is difficult to detect cubic terms in this rate equation. It was concluded that alkaline phosphatase does not obey Michaelis-Menten kinetics. Rather, the steady state data require a mechanism of at least second degree but do not exclude a rate equation of third degree.

Alkaline Phosphatase↗
PubMed1988

Comparison of an inductively coupled plasma-atomic emission spectrometry method for the determination of calcium, magnesium, sodium, potassium, copper and zinc with atomic absorption spectroscopy and flame photometry methods.

Serum calcium, magnesium, copper and zinc concentrations obtained from the analysis of 77 serum samples by inductively coupled plasma-atomic emission spectrometry (ICP-AES) are compared with the results obtained using atomic absorption spectroscopy (AAS). Similarly, serum sodium and potassium levels from the analysis of the same samples by ICP-AES are compared with the levels obtained by flame photometry. For each metal, we compare the results from both methods with a linear regression program that assumes error in both variables. The regression analysis shows that the ICP-AES method gives slightly higher calcium, copper, and zinc results and lower magnesium results than the AAS methods, and lower sodium and potassium results than the flame photometry method. Except for sodium, the correlation (r) between the results is very high (greater than or equal to 0.958), indicating that the ICP-AES results could be corrected to be equivalent to the atomic absorption or flame photometry results. The ICP-AES has the advantage of requiring less preparation and analysis time, and additional elements could be determined simultaneously in the same sample.

Blood Specimen Collection↗
PubMedDate not supplied

SEQUAL: an interactive computer program for sequential classification of biomedical data.

A computer program for sequential bayesian classification of patterns defined by integer and real-valued data is described. Classified patterns from a training sample are used to estimate the non-parametric (kernel) probability density functions and the a-priori class probabilities necessary to implement the bayesian classification. For each pattern and at each step in the sequential program, the 'best' feature to be measured at the next step is computed on the basis of the estimated misallocation error rate. The user can actually use the proposed feature or any other one; once the chosen feature has been measured, its value is used to allocate the pattern into the class with the highest conditional a-posteriori probability, according to the Bayes formula. The main feature of the program consists in the computation of the 'probability of reversal' at each step of the sequential procedure. The probability of reversal represents the probability that at the next step the pattern will be classified into a class different from the present one. The probability of reversal can be used as a stopping criterion, which is more efficient than other commonly used stopping rules, such as the a-posteriori Bayes probability or the estimated misallocation error rate. The program, available in FORTRAN 77 for a VAX/VMS machine, has been tested both on simulated and real data collected from patients suffering from various forms of hepatic disease.

Bayes Theorem↗
PubMed1989

Comparison of Bayesian with group sequential methods for monitoring clinical trials.

We describe some problems with applying methods based on classical sequential analysis to monitoring clinical trials. A Bayesian method is developed and the boundaries are compared with frequentist schemes. For the examples chosen, the Bayesian boundaries can be quite similar to those obtained from Pocock and O'Brien and Fleming (OBF) rules, depending on the choice of prior distribution. They converge less rapidly than OBF's but more rapidly than Pocock's. In general the Bayesian methods provide the same desirable features as frequentist methods, without sacrificing flexibility and simplicity of interpretation.

Bayes Theorem↗
PubMed1989

Analyses of group sequential clinical trials.

In the first part of this article the methodology of group sequential plans is reviewed. After introducing the basic definition of such plans the main properties are shown. At the end of this section three different plans (Pocock, O'Brien-Fleming, Koepcke) are compared. In the second part of the article some unresolved issues and recent developments in the application of group sequential methods to long-term controlled clinical trials are discussed. These include deviation from the assumptions, life table methods, multiple-arm clinical trials, multiple outcome measures, and confidence intervals.

Actuarial Analysis↗
PubMed1989

Kinetic studies of chloride inhibition in aspartate aminotransferase activity.

The inhibitive effects of chloride anion on the activity of mitochondrial aspartate aminotransferase (L-aspartate: 2-oxoglutarate-aminotransferase EC. 2.6.1.1.) from chicken (Gallus domesticus) and turkey (Maleagris gallopavo) were studied. Steady-state velocities were obtained from a wide range of chloride concentrations. The data were fitted by rational functions of 0:2 and 1:2 for chloride, using a non-linear regression program which guaranteed the fit. The goodness of fit was improved by the use of a computer program that combined model discrimination, parameter refinement and sequential design. It was concluded that chloride aspartate aminotransferase inhibition requires a minimum velocity equation of 1:2 with regard to chloride, and a plausible kinetic mechanism for this experimental result was proposed.

Animals↗
PubMed1981

Elimination and replenishment of tricarboxylic acid-cycle intermediates in myocardium.

1. The contribution of Co2 fixation to the anaplerotic mechanisms in the myocardium was investigated in isolated perfused rat hearts. 2. K+-induced arrest of the heart was used to elicit a transition in the concentrations of the intermediates of the tricarboxylic acid cycle. 3. Incorporation of 14C from [14]bicarbonate into tricarboxylic acid-cycle intermediates was measured and the rates of the reactions of the cycle were estimated by means of a linear optimization program which solves the differential equations describing a simulation model of the tricarboxylic acid cycle and related reactions. 4. The results showed that the rate of CO2 fixation is dependent on the metabolic state of the myocardium. Upon a sudden diminution of cellular ATP consumption, the pool size of the tricarboxylic acid-cycle metabolites increased and the rate of label incorporation from [14C]bicarbonate into the cycle metabolites increased simultaneously. The computer model was necessary to separate the rapid equilibration between bicarbonate and some metabolites from the potentially anaplerotic reactions. The main route of anaplerosis during metabolite accumulation was through malate + oxaloacetate. Under steady-state conditions there was a constant net outward flow from the tricarboxylic acid cycle via the malate + oxaloacetate pool, with a concomitant anaplerotic flow from metabolites forming succinyl-CoA (3-carboxypropionyl-CoA).

Animals↗